IPA: /ˌɪntrəˈsɛljʊləli/
KK: /ɪntrəˈsɛl.jʊ.lər.li/
In a way that occurs within a cell.
The drug works intracellularly to target the disease.
Intracellularly is formed from "intra-" (meaning within) and "cellula" (from Latin, meaning small room or cell) and the suffix "-ly" (meaning in a manner). The word describes something that occurs within a cell.
Think of 'intra-' meaning 'within' and 'cellula' meaning 'cell' — so intracellularly refers to processes happening within a cell.