No, they are not. There are many nouns that end in the letter s that are not plural, including the ones below.
Dress
Boss
Truss
Compass
Penis
Iris
Nexus
Thesis
Ellipsis
Mantis
Some words are singular even though they end in 'es', like
molasses
No, nouns ending in 's' are not always plural; some examples are:abacusabyssaddressasparagusbassbiasbonusbuscactuscallouscampuscircusclasscompasscosmosdaisdiabetesdiscusdressemphasisethosficusfocusfungusgasgeniusglassgrasshaggishepatitishiatushibiscushippopotamushummusibisisthmuskisslasslenslossmantismessmetropolismolassesmossnemesisnexusnucleusoasisoctopusonusosmosispantsparenthesispasspelvisphysicsplatypuspluspressprogresspusradiusrhesusruckussassafrassisstatusstratusstresssuccesssurplussynopsistennisTexastrellistrussviruswalruswatercresswellnesswitnessyes
Try writing this question in English. Most plural nouns do end in s. Perhaps you mean that you want a list of nouns that end in s but are not plural.
The plural form for the proper noun Lois is Loises.singular nouns ending in 's' form the plural by adding 'es' to the end of the word.The plural possessive form is Loises'.plural nouns that end in 's' add an apostrophe after the ending 's' to form the possessive.
Pants, scissors, pyjamas, species, spectacles, gallows, tongs, trousers, jeans are examples of nouns ending in 's' that are always plural
The possessive of all English plural nouns NOT ending is -s is 's: feet's
The plural is valleys.Unlike nouns ending in -y (ally, spy), English nouns ending in -ay or -ey form regular S plurals.
The possessive of all English plural nouns not ending in -s is formed by adding -'s: oxen's
The correct plural possessive form of "man" is "men's."
The possessive form of the plural noun cars is cars'.The possessive of all plural English nouns ending in -s is formed by adding an apostrophe after the ending -s.
Pianos Cellos Piccolos
Proper nouns ending in -s are made plural by adding -es to the end of the word; for example: The Jenningses
The possessive of all English plural nouns ending in -s is formed by adding an apostrophe: knives'