opuscule
Concise Oxford English Dictionary © 2008 Oxford University Press:
opuscule /əˈpʌskjuːl/ (also opusculum /əˈpʌskjʊləm/)
▶noun (pl. opuscules or opuscula /-lə/) rare a small or minor opus.
– origin C17: from Fr., from L. opusculum, dimin. of opus ‘work’.
'opuscule' also found in these Oxford entries:

