ABC is somehow fundamental (5)
I believe the answer is:
basic
'fundamental' is the definition.
(similar in meaning)
'abc is somehow' is the wordplay.
'somehow' indicates an anagram.
'abc'+'is'='abcis'
'abcis' anagrammed gives 'BASIC'.
(Other definitions for basic that I've seen before include "Rudimentary - programming language" , "Fundamental, forming a starting point" , "Without frills" , "Fundamental, underlying" , "Straightforward" .)