Flightless may be thought of as denotional, diachronically, if it implied the wings. PS: Compare especially Luxemburgish Fliicht "wing". Likewise Dutch vleder
From Old Dutch fledarôn, from Proto-Germanic *fleþarô (“wing”), probably related to *fifaldǭ (“butterfly”). Related to the first element of German Fledermaus (“bat”), which corresponds to modern Dutch vleermuis.
In the synchronic sense, it might or might not be connotative.
I quote @jlawler
Denotation meaning and connotation meaning are not technical terms in semantics. Connotation is a cover term for many different kinds of pragmatic and semantic phenomena, and is generally insufficiently specific to be useful. Basically, everything we think of as "meaning" is "connotation", unless we are logicians.
– jlawler 13 hours ago
... and myself for context
Indeed, I'd rather have denotation be the implication of an actual object, i.e. a word that can be depicted with a symbol. This does rather not work for flightless, and in principle not for anything -less. Cororally, if you have to catch a flight, this is invariably denotional of the plane, and the activity is a connotation. This is curious, compared to German Flucht which describes the abstract (to flee "flüchten", Flucht "flight", but Flug "flight", fliegen "to fly"), but also rather concretely an avenue, or border (mostly in construction); Flugzeug might reflect the -t
– vectory 2 mins ago
Following @yellowsky, it would be denotational even if denoting the activity of flying, or the result of flight, but this necessarily implies that all words are denotational in all senses, if, quite simply, words just mean what they are supposed to mean.
Insofar my understanding of denotation leads to cognates, it must be pretty good. Perhaps that's useless to you, your question isn't abundantly clear.