The word "laugh" exists in English, but not "*daugh", even though both have a -ter word and their forms are similar.
I can't find the function of the morpheme "-ter" here, which may be irrelevant to the "-ter" in "enter" or "utter", which are a comparative suffix (from PIE *-tero) and a frequentative suffix "-er"(of unknown origin to me), respectively.
There was the agent suffix -ter- of PIE. It was used for creation of terms for relatives and for creation of agent nouns.
Suffix -ter- was used to create a noun for person whose function or profession was to perform the action (irrespective whether he actually did it) while the o-grade of it -tor- was used to denote a person who just did the action. The combination of suffixes -a̯-ter- was used for some relatives.
Thus the term for daughter in PIE was dhuga̯tēr.
The same suffix in zero-grade, "-tr-" in combination with inanimate ending "-om" was used for creating words for tools, such as a̯ero̯trom "plow", u̯estrom "wear", tere̯trom "auger", costrom "knife".
Thus regular PIE rules suggest that a combination of the root for laugh, "kleg-" plus "-tr-" such as in "klegtrom" should give a non-animate noun related to laugh. In Pre-Germanic the ending could change from inanimate -om to masculine -os to render (via metathesis) *hlahtraz in Proto-Germanic.
It is more possible though that the word by this same process was formed already after Germanic branch split of PIE because other branches do not show use of the -tr- suffix with this root.
By the way, of course, the PIE superlative -ter-os was also another use of the same suffix. Thus "gela̯teros" would mean "more joyful". The word "enter" (from Latin intra-) is another example of use of this suffix with adverbs: e̯en "in" + "-ter-om" -> e̯enterom "intestines", of which locative case is e̯enteri "inside".
Would it be much of a leap to suggest this as an example of a "cranberry morpheme"? A somewhat fossilised style of inflection, in that it no longer carries any distinct meaning in itself, but nonetheless is still quite pertinent to the meaning of the the word itself.
I've also put a little more thought into it and have come up with daughter, sister, from English, as well as mater and pater from Latin as examples of famillial relations employing -ter.
Even with English being a third language to me, the grammatical purport of the suffix "-ter" in words such as "laughter" is easily deducible with only a second's worth of though expended. The affixation of "-ter" is an obvious, though uncommon from my experience, inflectional suffix serving to change a verb, as in "laugh", into a noun. Compare "He laughed at the joke I had told him..." to "His laughter at the joke I had told him...".
