If I want to describe that the word philosophia was borrowed from Greek to Latin, which Latin verb can I use for borrowing? Verbs like commodare and mutuari sound a little weird for this kind of loan. Should I go with a simple sumere or something else?
In Instutio oratoria 1.4.7–8, Quintilian uses the verb mutuor to talk about how the letters Y and Z are 'borrowed' into the Latin alphabet to render some Greek words (text and translation from the Perseus website):
an cuiuslibet auris est exigere litterarum sonos? non hercule magis quam nervorum. at grammatici saltem omnes in hanc descendent rerum tenuitatem, desintne aliquae nobis necessariae litterarum, non cum Graeca scribimus (tum enim ab iisdem duas mutuamur) sed propriae, in Latinis, ut in his seruus et uulgus Aeolicum digammon desideratur, et medius est quidam V et I litterae sonus; non enim sic optimum dicimus ut opimum, et in here neque E plane neque I auditur.
It is not every ear that can appreciate the correct sound of the different letters. It is fully as hard as to distinguish the different notes in music. But all teachers of literature will condescend to such minutiae: they will discuss for instance whether certain necessary letters are absent from the alphabet, not indeed when we are writing Greek words (for then we borrow two letters from them), but in the case of genuine Latin words: for example in words such as seruus and uulgus we feel the lack of the Aeolic digamma; there is also a sound intermediate between u and i, for we do not pronounce optimum as we do opimum, while in here the sound is neither exactly e or i.
If mutuor can be used to talk about borrowing individual letters in order to transliterate a Greek word, perhaps it follows that an entire Greek word that has been thus transliterated can also be said to be borrowed.
(However, as I note in my comment to the original question, in most other passages where the verb mutuor is used in the context of words, it appears to describe the process of deriving brand-new words – or expanding the range of meanings of existing words, in the case of Quintilian 10.1.13 – on the basis of some other word and, in this way, 'borrowing' from that other word.)
The primary meaning of 'borrow' in English is to use something with the intention of returning it after use, and the verb is thus the correlative of 'lend'. In a separate idiom, the word is used entirely properly, but to mean something like 'convert' or 'appropriate'.
That doesn't mean that there is no single Latin word that is exactly suitable for both cases. The verb mutuor, indeed, has the exact sense of the English, either as the correlative of 'lend', or simply to 'adopt', or 'take for one's own use' etc.