Fortunately there are some rules that hold fairly well. In final clusters, after a voiced consonant we always get z: fibs, adds, begs, slams, hens, tells. The -s is almost always inflectional, but the rule still works when it isn’t: lens lenz.
This is why newsreaders and others tend to mispronounce the name of the city of Homs, now in the news. As the Oxford BBC Guide to Pronunciation reminds us, it is properly hɒms, rather than the hɒmz we often hear. The only way this could be clearly signalled in English spelling would be if we were to write Homss.
In Arabic it’s actually حيمص Ḥimṣ ħimsˁ, with a final voiceless ‘emphatic’ (pharyngealized) alveolar fricative. The city was previously known as Emesa (Greek Ἔμεσα), again with a voiceless fricative.
I notice that in the Japanese Wikipedia it’s ホムス homusu, not ホムズ homuzu. Quite right.
I have known the word cowslip, the name of a wildflower, from an early age, and have always pronounced it ˈkaʊslɪp. As far as I know, so does everyone else. The s here does not trigger pre-fortis clipping, so it is natural to analyse the word as cow plus slip.
Recently I had a sudden thought: is it really from cow’s plus lip? Does the flower or its leaf look like part of a bovine mouth? (There’s another, similar, flower called an oxlip.) That would make the fricative an inflectional z. Are there, or were there, people who say ˈkaʊzlɪp?
But no. The OED tells us that its etymology is
Old English cú-slyppe, apparently < cú cow + slyppe viscous or slimy substance, i.e. ‘cow-slobber’ or ‘cow-dung’ (compare German kuh-scheisse as a plant-name in Grimm)
It’s got nothing to do with a cow’s lip. Where the cow slips, there slip I.