IPA: /ˌsʌb.kjuː.təˈneɪ.əs.li/
KK: /sʌbˈkjutənəsli/
In a way that occurs beneath the skin's surface.
The medication was administered subcutaneously to ensure quick absorption.
Subcutaneously → It is formed from "sub-" (meaning under) and "cutis" (meaning skin) and the suffix "-ly" (meaning in a manner). The word describes something that occurs in a manner that is under the skin.
Think of something happening 'under' ('sub-') the 'skin' ('cutis') — that's why subcutaneously refers to actions or processes that take place beneath the skin.