-iaan /i'ja:n/ and -aan /'a:n/ are stress-bearing non-native cohering suffixes forming nouns. De Haas and Trommelen (1993: 193 ff) distinguish three subtypes:

• There is a group of person's names of common gender, taking the definite singular article de, in -iaan or -aan. Two subgroups can be distinguished:
  • The suffix is -iaan in words such as Heideggeriaan that are based on family names. The meaning is (male) supporter or follower of the base, the proces is productive: new forms such as Bieberiaan fan of youth idol Justin Bieber are attested. Rarely one finds feminine forms constructed with the suffix -e (e.g. multatuliane female follower of (writer) Multatuli (Eduard Douwes Dekker, 1820-1887)).
  • The suffix is -aan in words of common gender such as franciscaan franciscan and brahmaan brahman that are based on first names (Franciscus and Brahma, respectively). The meaning is (male) supporter or follower of the base, member of a religious order, adherent of a confession; new forms are very rare. Feminine forms are by means of the suffix -es in the case of Christian religious orders (franciscanes), otherwise in -se, as in mohammedaanse female muslim, probably a nominalization of the pertinent adjective mohammedaans muslim.
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    De Haas and Trommelen (1993: 194) point out that final schwa in the base is deleted: Thorbeckiaan < Thorbecke, Reviaan < Reve; this follows from the general rule of pre-vocalic schwa deletion. Occasionally, other parts of the base name are deleted: Aristoteliaan < Aristoteles Aristotle, Arminiaan < Arminius, Lubberiaan < Lubbers, Franciscaan < Franciscus St. Francis. They point at formations such as anglicaan, parochiaan, diocesaan, kapelaan Anglican, parishioner, diocessan, chaplain that may or may not be formed with the same suffix. The flower name gentiaan gentian is a loan from Latin (Etymologiebank).

• The suffix -aan is quite common in deriving geographical person names of common gender, especially if the base name ends in -a, which gets deleted (Amerikaan < Amerika, Bogotaan < Bogotá, indiaan indian < India) or ië, where we get pre-vocalic schwa deletion (Venetiaan someone from Venice < Venetië Venice, Brazilian < Brazilië Brazil). In general, however, the choice of the geographical suffix is unpredictable. Feminine counterparts are formed by means of the suffix -se: Amerikaanse, Bogotaanse.
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  An alternative analysis of the feminine forms Amerikaanse, Bogotaanse is as nominalizations of the pertinent adjective, which is quite common in the case of female inhabitant names.

• There is another use of -aan (never -iaan) in names of chemical compounds like ethaan ethane, C2H6 and isopentaan isopentane, 2-methylbutane, C5H12, which are mass nouns of neuter gender. The suffix's meaning contribution is saturated straight-chain hydrocarbon (Affixes.org). Plurals are in -en, but rare.

In all cases, the suffix bears the main stress. Person-denoting (i)aan derivations can have a plural in -en, a diminutive in -tje, and can be input for adjective derivation by means of the suffix -s (Heideggeriaans, Bieberiaans, Mohammedaans, Amerikaans).