Unite under pressure, perhaps, getting married outside Lima (4)
I believe the answer is:
weld
'unite under pressure perhaps' is the definition.
(as in welding things together)
'married outside lima' is the wordplay.
'married' becomes 'wed' (wed can mean married).
'outside' is an insertion indicator.
'lima' becomes 'L' (phonetic alphabet: alpha, bravo, charlie etc.).
'wed' going around 'l' is 'WELD'.
'getting' acts as a link.
(Other definitions for weld that I've seen before include "Fused metal joint" , "Join using fusion" , "Join intimately together" , "Join by fusion; dye plant" , "Bond" .)