I challenge you to produce an etymological relationship, rather than a Freudian one, between penis and pencil (#8)
Etymology: < Anglo-Norman and Old French, Middle French pincel paint-brush (c1165 as peincel ; French pinceau ) < an unattested post-classical Latin form *penicellus , alteration (with suffix substitution) of classical Latin pēnicillus paint-brush, pictorial art, also a swab, pad (compare penicil n. 1) < pēniculus brush ( < pēnis tail (see penis n.) + -culus -cule suffix) + -illus (see -illa suffix). Compare post-classical Latin pincellus, pincillus (from c1125 in British sources), Old Occitan pinsel (c1200 as pinzell; Occitan pincèl), Catalan pinzell (1351), and Spanish pincel (early 13th cent. as pinzel, probably < either Catalan or Old Occitan).
The French word was also borrowed into other Germanic languages: Dutch penseel paint-brush, pencil, Middle High German pensel , pinsel paint-brush, brush (German Pinsel ; > Old Swedish pinzil (Swedish pänsel), Danish pensel ).
And see #14.
Admittedly, they’re not “transparently etymologically related” (your rule), but then, what is? Are “vicarage” and “vicarious” (in many people’s minds) transparently related? Are “indigent” and “indigene” transparently etymologically related in some people’s minds (incorrectly)?
---E. “pen” isn’t etymologically related to "penis," of course, not even the fountain pen, but derives from L. penna, feather.