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
Some examples of plural nouns not ending with 's' are children, men, women, mice, and geese.
Some examples of plural nouns ending in "s" include books, dogs, cats, cars, and trees.
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.
Pants, scissors, pyjamas, species, spectacles, gallows, tongs, trousers, jeans are examples of nouns ending in 's' that are always plural
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 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.
The possessive of all English plural nouns NOT ending is -s is 's: feet's
Pianos Cellos Piccolos
It really depends. If this is purely English, then it may just use the English 's' plural ending. If, however, it is Latin-derived, it is then most likely going to end in -ae (which is the Latin first-declension plural ending).
Most nouns form the plural by adding -s or -es week / weeks toy / toys bus /buses Some noun are irregular, their plurals are another word: foot / feet child / children woman /women