Lengthy word? Interminable, perhaps? (4-4)
I believe the answer is:
long-term
'interminable perhaps?' is the definition.
I can't tell whether this definition defines the answer.
'lengthy word?' is the wordplay.
'lengthy' becomes 'long' ('long' can be a synonym of 'lengthy').
'word?' becomes 'term' (term is a kind of word).
'long'+'term'='LONG-TERM'
Can you help me to learn more?
(Other definitions for long-term that I've seen before include "Relating to a relatively extended period" , "Not immediate" , "Over a great time" , "Enduring" .)