The connecting letter should be able to create a valid word acceptable in the Scrabble game.
Because there is no standard rule for words ending in -o.
Please see the related question.
The plural of rule is rules.
"Chief" is a singular noun with its own unique plural form, which is "chiefs." It follows the standard rule for forming plurals in English, where most words simply add an "s" to show they are in plural form.
Some examples of hard words that have irregular plurals are: oxen, children, criteria, and phenomena. These words do not follow the typical rule of adding "s" or "es" to form their plural form.
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.
Certain words, such as qi, have made it into the SCRABBLE dictionary, but as a general rule, all words must be in English to be valid.
The plural form of traffic rule is traffic rules.
Swaraj -- self-governance or "home-rule".
The regular plural form of a noun adds (s) or (es) to the singular noun.
The normal rule for singular, countable nouns ending in -LF is to change the F to V and add -ES, as in the words half, self, and wolf (halves, selves, wolves). However, gulf is the exception to the rule, because its plural is gulfs.
Words like half (halves), wife (wives), dwarf (dwarves), hoof (hooves).