in ‧ fin ‧ i ‧ tes ‧ i ‧ mal /ˌɪnfɪnəˈtesəm ə l◂, ˌɪnfɪnɪˈtesəm ə l◂/ BrE AmE adjective
[ Date: 1600-1700 ; Language: Modern Latin ; Origin: infinitesimus 'infinite in rank' , from Latin infinitus ]
extremely small SYN minuscule :
infinitesimal changes in temperature
—infinitesimally adverb :
infinitesimally small