Adjektive: Grundkongruenz und starke Deklination

An English adjective stays the same: "a tired man, a tired woman, tired children". An Icelandic adjective agrees with its noun in gender, number and case. Here is fallegur (beautiful) in the strong forms you use with a noun that has no article:

Three endings carry most of the load at this stage: -ur for a masculine subject, nothing for a feminine one, -t for neuter. Góður (good) follows the same pattern but its neuter is gott: góður dagur, góð bók, gott kvöld.

Small changes in the stem

• Some adjectives whose stem ends in -r, such as stór (big) and dýr (expensive), take no extra -ur: stór hestur (a big horse), not *stórur; neuter stórt hús.
• An a in the stem turns into ö in the feminine nominative singular: svangur → svöng (hungry), langur → löng (long). A woman says Ég er svöng.

After the verb "to be" it still agrees

English speakers remember agreement before a noun and forget it after vera. In Icelandic the adjective agrees there too: Hann er þreyttur. Hún er þreytt. Barnið er þreytt. Þau eru þreytt. - He / she / the child / they are tired. Húsið er stórt. - The house is big.

The adjective goes before the noun, as in English: íslenskur hestur, heitt kaffi (hot coffee). With the suffixed article it switches to a separate weak set of endings, as in Bláa lónið (the Blue Lagoon); that is a topic of its own.