Old Irish class B III verbs (McCone's S1d) are inflected just like class B I, but the present stem always ends in ng, and the n disappears in the other stems. (There is one verb whose stem ends in nd, namely roindid (“to redden”).) These verbs are derived from Proto-Indo-European verbs with the nasal infix *-né-. They correspond to Latin verbs like tangō (perfect tetigī, past participle tāctus) and Sanskrit class 7 verbs like युनक्ति (yunakti) (perfect युयोज (yuyoja), past participle युक्त (yukta)).
There are apparently no deponent verbs in this class.
Because of a sound change in Proto-Celtic, the root vowel in this class is i rather than e when the following consonant cluster is palatalized, e.g. dingid, dringid. However, most verbs in this class actually have the root vowel o and often show a lack of palatalization of the stem-final consonant cluster (e.g. bongaid, tongaid).
See Category:Old Irish class B III present verbs for a list of verbs belonging to this class.
The basic pattern is shown by dingid (“to thrust”). The endings are as follows:
| 1st sg. | 2nd sg. | 3rd sg. | 1st pl. | 2nd pl. | 3rd pl. | Passive singular | Passive plural | |
|---|---|---|---|---|---|---|---|---|
| Absolute | dingu* | dingi* | dingid | dengmai | dingthe | dengait | dengair | dengtair |
| Conjunct | ·diung† | ·ding* | ·ding | ·dengam | ·dingid | ·dengat | ·dengar | ·dengtar |
| Relative | dinges | dengmae | dengtae | dengar | dengtar | |||
| *With i-affection (/e/ is raised to /i/) †With u-affection (/e/ is diphthongized to /iu̯/). | ||||||||
| 1st sg. | 2nd sg. | 3rd sg. | 1st pl. | 2nd pl. | 3rd pl. | Passive singular | Passive plural |
|---|---|---|---|---|---|---|---|
| ·dinginn | ·dingthea | ·dinged | ·dingmis | ·dingthe | ·dingtis | ·dingthe | ·dingtis |
| 2nd sg. | 3rd sg. | 1st pl. | 2nd pl. | 3rd pl. | Passive singular | Passive plural |
|---|---|---|---|---|---|---|
| ding | dinged | dengam | dingid | dengat | dengar | dengtar |
An example of a verb with depalatalization is tongaid (“to swear”), in which the ng cluster is depalatalized whenever a vowel follows:
| 1st sg. | 2nd sg. | 3rd sg. | 1st pl. | 2nd pl. | 3rd pl. | Passive singular | Passive plural | |
|---|---|---|---|---|---|---|---|---|
| Absolute | tongu | tongai | tongaid | tongmai | toingthe | tongait | tongair | tongtair |
| Conjunct | ·tung* | ·toing | ·toing | ·tongam | ·tongaid | ·tongat | ·tongar | ·tongtar |
| Relative | tongas | tongmae | tongtae | tongar | tongtar | |||
| *With u-affection. | ||||||||
| 1st sg. | 2nd sg. | 3rd sg. | 1st pl. | 2nd pl. | 3rd pl. | Passive singular | Passive plural |
|---|---|---|---|---|---|---|---|
| ·tongainn | ·toingthea | ·tongad | ·toingmis | ·toingthe | ·toingtis | ·toingthe | ·toingtis |
| 2nd sg. | 3rd sg. | 1st pl. | 2nd pl. | 3rd pl. | Passive singular | Passive plural |
|---|---|---|---|---|---|---|
| toing | tongad | tongam | tongaid | tongat | tongar | tongtar |
In a few cases, forms without n are found when the stem vowel is unstressed, e.g. ·eitig (third-person singular present prototonic) and ·eitegar (passive singular present prototonic) from as·toing (“to refuse”) or fo·coimlich (third-person singular present com-form) from fo·loing.