Short and sweet ending of Gaelic tongue (5)
I believe the answer is:
terse
'short and sweet' is the definition.
(thesaurus)
'ending of gaelic tongue' is the wordplay.
'ending of gaelic' becomes 't' (I can't explain this - if you can you should give a lot more credence to this answer).
'tongue' becomes 'erse' (Erse is an example).
't'+'erse'='TERSE'
Can you help me to learn more?
(Other definitions for terse that I've seen before include "Of speech, short and pithy" , "Crisply brief" , "Brusque and curt" , "Brusque, concise" , "Reset to be pithy" .)