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 the answer is hidden within the clue.
'LINGO' can be found hidden inside 'requires spelling out'.
(Other definitions for lingo that I've seen before include "French?" , "Jargon, language (colloq.)" , "Language (informally)" , "Argot" , "Johnny Foreigner speaks one" .)