Unfamiliar jargon requires spelling out, partially (5)
I believe the answer is:
lingo
'unfamiliar jargon' is the definition.
(I've seen this before)
'requires spelling out partially' is the wordplay.
'partially' indicates a hidden word.
'LINGO' is hidden within 'requires spelling out'.
(Other definitions for lingo that I've seen before include "French?" , "Jargon, language (colloq.)" , "Language (informally)" , "Argot" , "Johnny Foreigner speaks one" .)