There are two senses of caustic.

Sense 1:

acerb, acerbic, acid, acrid, bitter, blistering, caustic, sulfurous, sulphurous, virulent, vitriolic

unpleasant (vs. pleasant)

Sense 2:

caustic, corrosive, erosive, vitriolic, mordant

destructive (vs. constructive)

acerb, ardeb, carob, celeb, chimb, climb, clomb, coomb, crumb, demob, exurb, nawab, plumb, redub, rehab, rhomb, rhumb, sahib, scrub, shrub, slurb, squab, squib, throb, thumb, zineb

The word exacerbate sounds like this: ecks a sir bate. The a is a short vowel sound, like the a in man, plan etc.

According to SOWPODS (the combination of Scrabble dictionaries used around the world) there are 1 words with the pattern A-E-B. That is, five letter words with 1st letter A and 3rd letter E and 5th letter B. In alphabetical order, they are:

acerb