Subcutaneously describes how something is done: under the skin. It is the adverb, so it goes with a verb rather than with a noun. A drug is injected subcutaneously; fluids are given subcutaneously; fat is stored subcutaneously. You meet it above all in medicine instructions — 'Administer 10 units subcutaneously twice daily' is exactly the register it lives in. It is formal and technical, and it does not appear in ordinary conversation; a nurse chatting to a colleague would say 'give it sub-cut', and a patient would just say 'the injection goes in my tummy'. Because it is written more than spoken, learners often meet it first on a package insert or in a textbook. Say it in pieces and it stops being frightening: sub-cue-TAY-nee-us-ly.

以皮下方式（注射、給藥）；藥品說明上常寫「皮下注射」。