the -t- is organic

The word ‘simultaneous’ comes perhaps from simultim “at the same time,” extended from Latin simul “at the same time” (see similar (adj.)), or from simul with ending abstracted from Late Latin spontaneus, where the -t- is organic.

An organic -t-?I cannot understand its meaning. Please give me a hint.

I believe it’s just a way of classifying this particular phoneme (the ‘t’ sound) in this particular word.

I think the ‘t’ is part of ‘spontaneous’ (English>spont+aneous) and not of ‘simultaneous’ which is formed by ‘simul’ (Latin) and ‘taneous’ (instead of ‘aneous’); maybe, to avoid the otherwise possible term simulaneous/simulous using the suffix ‘aneous/ous’.