No, a compression driver & waveguide are not the same thing.
(Sweeping generalisations incoming...)
The compression driver is the bit with the magnet, voicecoil, diaphragm etc that actually produces the sound. It's usually intended to be used with a horn mounted to the front of it which both increases its efficiency and controls how widely the sound spreads out.
A waveguide is similar to a horn in that it mounts in front of a driver, but different in that its goal is mostly controlling the spread of sound, but not increasing efficiency.
A tweeter can be one of a couple of things - most commonly, a high frequency driver that does not need to be coupled to a horn or waveguide in order to work properly - such as the dome or ring tweeters in most hifi cabs.
It can also refer to a complete driver + horn/waveguide assembly.
HTH,
David.
(Sweeping generalisations incoming...)
The compression driver is the bit with the magnet, voicecoil, diaphragm etc that actually produces the sound. It's usually intended to be used with a horn mounted to the front of it which both increases its efficiency and controls how widely the sound spreads out.
A waveguide is similar to a horn in that it mounts in front of a driver, but different in that its goal is mostly controlling the spread of sound, but not increasing efficiency.
A tweeter can be one of a couple of things - most commonly, a high frequency driver that does not need to be coupled to a horn or waveguide in order to work properly - such as the dome or ring tweeters in most hifi cabs.
It can also refer to a complete driver + horn/waveguide assembly.
HTH,
David.
Thanks! 
Beat me to it, but is the better of the two WRT 'simple', so for a slightly more technically advanced 'simple'.............
For 'simple', only read what's in bold. The rest is for the folks that want a bit better understanding of this somewhat confusing subject.
A compression driver at its most basic is typically a 4th order band pass speaker (BP4), i.e. a driver boxed in with a sealed rear (compression) chamber and a front (acoustic low pass filter) chamber. Its design bandwidth (BW) based on this interactive chart determines whether it's a (sub) bass, (mid) bass, mids, HF driver.
When looking at a typical compression driver's cutaway though, due to its design it appears that the tiny gap between the diaphragm and phase plug is the compression chamber, but technically it's not, it's just a tiny low pass filter that has been 'compressed' to raise its resonance (Fb) up into the mids or HF since horns are historically designed based on the design BW's mean.
A waveguide (WG) is just that, it only controls directivity (polar response) whereas a expo, etc., (compression) horn actually increases gain over 'X' BW depending on its flare (expo, etc.), (design) frequency (horn cutoff/Fc) factor.
A tweeter is just that, a high frequency speaker be it a typical point source (frame) driver or a compression driver tweeter horn.
Beat me to it, but is the better of the two WRT 'simple', so for a slightly more technically advanced 'simple'.............For 'simple', only read what's in bold.
The rest is for the folks that want a bit better understanding of this somewhat confusing subject.A compression driver at its most basic is typically a 4th order band pass speaker (BP4), i.e. a driver boxed in with a sealed rear (compression) chamber and a front (acoustic low pass filter) chamber. Its design bandwidth (BW) based on this interactive chart determines whether it's a (sub) bass, (mid) bass, mids, HF driver.
When looking at a typical compression driver's cutaway though, due to its design it appears that the tiny gap between the diaphragm and phase plug is the compression chamber, but technically it's not, it's just a tiny low pass filter that has been 'compressed' to raise its resonance (Fb) up into the mids or HF since horns are historically designed based on the design BW's mean.
A waveguide (WG) is just that, it only controls directivity (polar response) whereas a expo, etc., (compression) horn actually increases gain over 'X' BW depending on its flare (expo, etc.), (design) frequency (horn cutoff/Fc) factor.
A tweeter is just that, a high frequency speaker be it a typical point source (frame) driver or a compression driver tweeter horn.