Lament unknown by the Spanish, for example (5)
I believe the answer is:
elegy
'lament' is the definition.
(I know that lament can be written as elegy)
'unknown by the spanish for example' is the wordplay.
'unknown' becomes 'y' (algebra).
'by' means one lot of letters go next to another.
'the spanish' becomes 'el' ('the' in Spanish).
'for example' becomes 'e.g.' (short for 'exempli gratia', 'for example' in Latin).
'el'+'eg'='eleg'
'y' put after 'eleg' is 'ELEGY'.
(Other definitions for elegy that I've seen before include "Sad work" , "Poem penned beside church" , "Plaintive poem" , "Sorrowful poem/song" , "Song of lamentation" .)