Certain nouns in Latin have an i-stem, such as puppis, -is (ship). However, following the consonant declension, these generally take an accusative stem –em (puppem), not –im.
This post covers exceptions to that rule, by listing all cases where –im is retained
1. Greek nouns borrowed from the Greek third declension (consonant declension) with an i-stem.
- Paris -> Parim
- Adōnis -> Adōnim
- Busīris -> Busīrim
2. The following Latin nouns:
- amussis, -is (rule)
- būris, -is (plough-beam)
- cucumis, -is (cucumber)
- rāvis, -is (??)
- sitis, -is (thirst)
- tussis, -is (cough)
- vīs, -ī (force, power)
[n.b. on rāvis, -is…. I can’t find this in any online dictionary. Any clues?]
3. Adverbs in –tim, such as partim (in parts)
The –im ending is also found occasionally in the following words–
- febris, -is (fever)
- puppis, -is (ship)
- restis, -is (cord)
- turris, -is (tower)
- secūris, -is (axe)
- sēmentis, -is (sowing)
“and rarely in many other words,” say A&G. Damn poets…
The Essential AG: 75a-b
Latin for Addicts 
Been enjoying the tour of AG. Thanks! Re: ravis. Festus writes that “ad ravim” (from Plautus) means “ad raucitatem”. (tinyurl.com/au5f3uu)—PJB
My “New Handy Dictionary”, printed 1962 gives “ravis” as “hoarseness.” Looks like doctors are as much to blame as poets… maybe it was the handwriting, even back then.
Vis-a-vis Kathy’s comment ut supra:
http://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.04.0059%3Aentry%3Dravis
http://athirdway.com/glossa/?s=ravis
Glossa is a very fast implementation of L&S online. It only does headword search, but it does it quite well.
In Adler, chapter 30, I find the following.
Accusative usually in -em, sometimes in -im:
messis
Accusative more often in -im than -em:
febris
pelvis
puppis
Accusative regularly in -im (ones in the blog post not repeated):
basis
poēsis
paraphrasis
[…] For more on where the -im ending shows up, see this post. […]
I was surprised to learn that besides Paridem, also Parim (and Parin) existed… I like this blog!
Glad to hear it!