The general rule in English usage is that if the noun ends in a vowel followed by o you add an s; if it ends in a consonant followed by o you add es. There are, however, a number of exceptions to the latter rule: pianos, solos, photos, memos, etc.]
For an English plural, the answer is never. Some words ending in the letter 's' are made plural by adding 'es', such as one bus, two buses or one class, two classes.
Because "stimulus" is a Latin word. In Latin, most words ending in "-us" form the plural in "i". They keep this in English.
No, nouns ending in 's' are not always plural; some examples are:abacusabyssaddressasparagusbassbiasbonusbuscactuscallouscampuscircusclasscompasscosmosdaisdiabetesdiscusdressemphasisethosficusfocusfungusgasgeniusglassgrasshaggishepatitishiatushibiscushippopotamushummusibisisthmuskisslasslenslossmantismessmetropolismolassesmossnemesisnexusnucleusoasisoctopusonusosmosispantsparenthesispasspelvisphysicsplatypuspluspressprogresspusradiusrhesusruckussassafrassisstatusstratusstresssuccesssurplussynopsistennisTexastrellistrussviruswalruswatercresswellnesswitnessyes
you add es
Two plural words ending in '-s':table > tableschair > chairs
As with other words ending in consonant-Y, the plural is BURGLARIES.
The number of English words ending -es cannot be counted, because -es can indicate either a plural form or verb conjugation. It can also be part of the root word. The number would exceed thousands of words.
The -tti ending on words in Italian is "little" in English.
Some plural nouns that end with 'os' are:avocadosbanjosbarriosbongosechosegosflamingosghettosgigoloshaloshobosJellokangaroolassologosnachospatiosphotospianospiccolosradiosrhinossolosstudiostacostattoostriosvideoszeroszoos
The usual plural form for words ending in -f or -ef is to drop the f and add ves. There are exceptions to this rule where only an s is added to the end of the words.
Where: GreekWhy borrowed: There is a trend in English to use Greek words in psychology.Plural form: psychosesWhy: To form the plural of Greek words ending in -sis,change to -ses.
Because there is no standard rule for words ending in -o.