Meagre lines finally accepted by extra (6)
I believe the answer is:
sparse
'meagre' is the definition.
(thesaurus)
'lines finally accepted by extra' is the wordplay.
'finally' says to take the final letters.
'accepted by' indicates putting letters inside.
'extra' becomes 'spare' ('spare' can be a synonym of 'extra'**).
The final letter of 'lines' is 's'.
's' going inside 'spare' is 'SPARSE'.
(Other definitions for sparse that I've seen before include "One's not at all thick" , "In short supply" , "Not much" , "Meagre, thin on the ground" , "Thin on the ground, scarce" .)