▁in ▁early ▁references . ▁For ▁the ▁first ▁ 1 5 ▁miles ▁of ▁its ▁course ▁it ▁defines ▁the ▁border ▁between ▁North umber land ▁and ▁C umb ria . ▁ ▁Et ym ology ▁ ▁The ▁name ▁Ir thing ▁may ▁be ▁of ▁Brit ton ic ▁origin , ▁though ▁its ▁precise ▁et ym ology ▁is ▁uncertain . ▁The ▁last ▁part ▁of ▁the ▁name ▁is ▁from ▁– ï nn , ▁an ▁ad ject ival ▁and , ▁in ▁place - names , ▁to pon ym ic ▁suffix , ▁added ▁to ▁n oun s ▁or ▁ad ject ives . ▁The ▁first ▁part ▁may ▁be ▁ar th , ▁meaning ▁" a ▁bear " ▁( c . f . ▁Wel sh ▁ar th ). ▁Or ▁else , ▁the ▁first ▁part ▁of ▁the ▁name ▁could ▁either ▁one ▁of ▁two ▁elements ▁suff ixed ▁with ▁- ed , ▁an ▁early ▁C elt ic ▁nom inal ▁suffix ▁meaning ▁" h aving ▁the ▁quality ▁of .. ". ▁ ▁The ▁first ▁of ▁these ▁is , ▁* ar , ▁an ▁ancient ▁river - nam ing ▁element ▁imp lying ▁either ▁horizontal ▁motion , ▁" flow ing ", ▁or ▁else ▁" ris ing " ▁or ▁" spring ing ▁up " ▁( compare ▁I rt ). ▁The ▁second ▁possibility ▁is ▁* ī r , ▁meaning ▁" f resh , ▁clean , ▁pure ". ▁ ▁Geography ▁▁ ▁It ▁is ▁thought ▁that ▁before ▁the ▁last ▁gla cial ▁maximum ▁the ▁Ir thing ▁flow ed ▁into ▁the ▁South ▁Ty ne ▁valley ▁through ▁the ▁waters hed ▁near ▁Green head , ▁now ▁known ▁as ▁the ▁Ty ne ▁G