I am copying the relevant sections for imparisyllabic (ανισοσύλλαβα) nouns from a comprehensive reference work, i.e. Greek, A Comprehensive Grammar by David Holton, Peter Mackridge and Irene Philippaki-Warburton.
For masculine nouns (p. 61):
2.1.6 Imparisyllabic nouns in -άς, -ας, -ής, -ης, -ές, -ούς
Imparisyllabic nouns by definition have a different number of syllables in their singular and plural forms. The plural forms have an extra syllable and always end in -δες (nom., acc., voc.), -δων (gen.). The nominative singular of such nouns may be oxytone, as type (i) below, or paroxytone, as type (ii). Generally speaking, the stress remains on the same syllable in the plural as in the singular, and the plural ending -δες is added to the vowel of the singular ending. Exceptions will be discussed with the examples. A third type (iii) are proparoxytone; because of the rule that there cannot be more than two unstressed syllables at the end of a word (see Part I, Section 1.5.1), the stress moves one syllable forward in the plural.
Imparisyllabic masculine nouns include many nouns of foreign (especially Turkish) origin, many words denoting occupations, augmentatives in -άς, diminutives in -άκης and -ούλης, and proper names in -άς, -ής and -ης. Examples are given after each type.
(i) ο παπάς ‘priest’
Sg. Pl.
Nom. ο παπάς οι παπάδες
Acc. τον παπά τους παπάδες
Gen. του παπά των παπάδων
Voc. παπά παπάδες
Examples:
Sg. in -άς, pl. -άδες: αρακάς ‘pea(s)’, βοριάς ‘north wind’, βραχνάς ‘nightmare’, γαλατάς ‘milkman’, καλοφαγάς ‘gourmet’, κερατάς ‘cuckold’,
κουβάς ‘bucket’, λεφτάς ‘money-bags (= person)’, μπαλτάς ‘axe’, μπελάς ‘trouble’, μυλωνάς ‘miller’, παπλωματάς ‘quilter’, παράς ‘money’, σουγιάς ‘penknife’, σφουγγαράς ‘sponge-fisher’, φονιάς ‘murderer’, χαλβάς ‘halva’, χαλκιάς ‘coppersmith’, ψαράς ‘fisherman’, ψωμάς ‘baker’, and proper names such as Λουκάς, Σαμαράς
Sg. in -ής, pl. -ήδες: ατζαμής ‘inexperienced person’, καταφερτζής ‘wheedler, smooth operator’, καφετζής ‘coffee-house keeper’, μερακλής ‘connoisseur’, μπεκρής ‘drunkard’, μπογιατζής ‘decorator’, παλιατζής ‘second-hand dealer’, παπουτσής ‘shoemaker’, ταξιτζής ‘taxi-driver’, and proper names such as Κωστής, Παντελής, Pαγκαβής, Χατζής
Sg. in -ές, pl. -έδες: γλεντζές ‘fun-lover’, καναπές ‘sofa’, καφές ‘coffee’, κεφτές ‘meatball’, λεκές ‘spot, stain’, μεζές ‘hors d’oeuvre, titbit’, μενεξές
‘violet’, μιναρές ‘minaret’, πανσές ‘pansy’, πουρές ‘purée’, τενεκές ‘tin’, χασές ‘calico’, χαφιές ‘informer’ Sg. in -ούς, pl. -ούδες: παππούς grandfather’
And for feminine ones (p. 70):
2.2.5 Imparisyllabic nouns
Feminine imparisyllabic nouns may be compared to the masculine imparisyllabic nouns discussed in Section 2.1.6. Their plural always ends in -δες (nom., acc., voc.), -δων (gen.), and this ending is added directly to the nominative singular, which always ends in a vowel, either (i) -ά or (ii) -ού. The genitive singular adds -ς to the nominative form. These feminine nouns are always oxytone in their singular forms and the stress remains on the same syllable in the plural.
(i) η γιαγιά ‘grandmother’
Sg. Pl.
Nom. η γιαγιά oι γιαγιάδες
Acc. τη γιαγιά τις γιαγιάδες
Gen. της γιαγιάς των γιαγιάδων
Voc. γιαγιά γιαγιάδες
Examples:
κυρά ‘missus, madam’, μαμά ‘mummy’, νονά ‘godmother’, νταντά ‘nursemaid’, οκά ‘oka (obsolete measure of weight = 1280 grams)’
(ii) η αλεπού ‘fox’
Sg. Pl.
Nom. η αλεπού oι αλεπούδες
Acc. την αλεπού τις αλεπούδες
Gen. της αλεπούς των αλεπούδων
Voc. αλεπού αλεπούδες
Examples:
γλωσσού ‘gossiping woman’, μαϊμού ‘monkey (male or female)’, παραμυθού ‘storyteller’, πολυλογού ‘chatterbox’, υπναρού ‘sleepy-head’, and many other words referring to females and often corresponding to a masculine noun in -άς or -ής, e.g. φωνακλού ‘loud-mouthed woman’, φωνακλάς ‘loud-mouthed man’
Such words are mainly confined to non-formal use.
