Depending on the context, ‘diffuse‘ acts as an adjective or a verb.

More observation also failed to detect any trace of a tail or coma, the diffuse envelope of gas and dust that we expect around every comet. – The Guardian

Dif-fuse’. (adj) Spread out, dispersed.

The adjectival version of ‘diffuse’ has the stress on the second syllable, and it is pronounced with a distinct strong ‘s’ sound at the end: dǝ-fyoos!’.

It’s a film with seriousness and compassion, though a little lengthy and diffuse. Dramatic storm clouds gather and pass overhead without ever quite bursting into rain. – The Guardian

As a verb, ‘diffuse’ still has the stress on the second syllable, but it terminates with a soft ‘z’ sound: dǝ-fyoozz’.

Dif-fuse’. (v) Distribute broadly, disperse, percolate.

If one chemical moves faster than the other, then as they diffuse through the cells, they’ll create a pattern of different chemical concentrations. – Forbes (really)