Creamer is cream plus -er: the thing that does the cream job. Hold a picture of a coffee table. Somewhere on it is whatever turns the dark cup pale and soft. Sometimes that is the pale stuff itself, poured from a bottle or shaken from a packet. Sometimes it is the tiny sealed pot one serving arrives in. Sometimes it is the little the cream is poured from. The word points at whichever one is doing that job.
Wiktionary records creamer as cream + -er, with cream coming through Middle English creme from Old French cresme. The -er ending names the thing that does something, which is why one word ends up covering both the stuff and the vessel.
Wiktionary 記載 creamer 由 cream 加 -er 構成，cream 經中古英語 creme 來自古法文 cresme。-er 的作用是「做那件事的那個東西」，所以同一個字才會既指那份奶，也指裝奶的容器。
Wiktionary entry 'creamer' (kaikki:3f6f69a190036ae4:1398516162), supplied in the evidence packet.
Two branches
倒進杯子裡的那份奶
這一群把重點放在「被加進去的那份東西」上：你要的是它進到杯子裡以後的效果。
noun · B1
A white liquid or powder that you put into coffee or tea in place of milk or cream. It makes the drink paler and softer in taste, and it is usually made without any milk in it, so it keeps for a long time.
奶精
桌上裝奶的小容器
同樣是「負責奶的那個東西」，只是這次落在拿來裝、拿來倒的器皿上，而不是裡面的內容。
noun · B2
A small jug that you fill with cream or milk and set on the table, so that people can pour some into their own tea or coffee.
奶盅