وإن لم يكن معناه مستقلا فهو أداة
If its meaning is not independently intelligible, it is an adāh (a relational particle).
The signification of “min” (“from”) becomes definite through its relation to other terms, as in “min al-bayt” (“from the house”). Uttered in isolation, it does not express the complete relation intended in that construction.
Grammar commonly calls this a ḥarf, while the logical division uses ism, kalimah and adāh. The sciences employ different classificatory purposes; their technical labels should be distinguished.