the smallest unit of meaning in a language...

Meaningful. To paraphrase, morpheme is the smallest meaningful unit in a language.

Jackson6612 wrote:

I was wondering that what would be a meaningless unit then?

One can divide a word into any parts he wants, meaningful or meaningless. And when the part (unit) is meaningless, you cannot call it a morpheme.

 

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For your reference:

morpheme: A meaningful linguistic unit consisting of a word, such as man,  or a word element, such as  -ed  in  walked,  that cannot be divided into smaller meaningful parts. (copy from American Heritage Dict. )

A morpheme is the carrier a sememe. (My comprehension)

sememe:  the meaning expressed by a morpheme. (copy from American Heritage Dict. )

But if you happen to read linguistic essays, you'll probably find that sometimes (if not often) the authors divide an item of the meanings of a word into several smaller sub-meanings, which are also called sememes. (My observation)

CalifJim wrote:

what would be a meaningless unit then? In English, k is a meaningless unit of language. lp is a meaningless unit of language. vop is a meaningless unit of language.  An English speaker would not be able to assign any meaning to such units.  To an English speaker there is nothing in the real world that is referred to by k or lp or vop. CJ

But in the following definition even s is considered a meaningful unit. What do you say about it?

morpheme
the smallest unit of meaning in a language. The words 'so', 'the' and 'boy' consist of one morpheme. 'Boys' consists of two morphemes, 'boy' and 's'.

But in the following definition even s is considered a meaningful unit. What do you say about it?

I say the same as GG did.  The s is considered meaningful at the end of a noun.  Its meaning is "more than one".  Another very short morpheme is n.  At the end of some irregular verbs it makes the past participle:  show, shown; take, taken.  As GG said, sometimes a particular sound like s (or n) is a morpheme; sometimes it isn't; it's only a morpheme when it has a meaning.

CJ